KR20160061175A - Piezoelectric ceramics composition, piezoelectric element, and method for the same - Google Patents

Abstract

The present invention relates to a piezoelectric ceramic composition in which at least one among LiCO_3, CaCO_3, PbO, CuO, and Fe_2O_3 is added as a sintering aid to a basic composition of (1-x)Pb(Mg_1_/2W_1_/2)_0.03(Ni_1_/3Nb_2_/3)_0.09(Zr_yTi_1_-y)_0.88O_3 + xBiFeO_3 (x=0 or 0.015, y=0.47 to 0.53), a piezoelectric element containing the composition, and a method for producing the same. The composition for piezoelectric ceramics according to the present invention can be sintered at a low temperature. The piezoelectric ceramics that is produced by the use of the same is improved in terms of structural, piezoelectric, and dielectric characteristics.

Description

TECHNICAL FIELD [0001] The present invention relates to a piezoelectric ceramic composition, a piezoelectric device, and a method of manufacturing the piezoelectric ceramic composition. [0002] PIEZOELECTRIC CERAMICS COMPOSITION, PIEZOELECTRIC ELEMENT, AND METHOD FOR THE SAME [

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric ceramic composition, a piezoelectric element and a manufacturing method thereof.

Typical piezoelectric ceramics used for laminated piezoelectric devices such as piezoelectric actuators, piezoelectric resonators, and piezoelectric filters include an internal electrode layer made of an Ag-Pd alloy and a ceramics layer made of a PZT piezoelectric ceramics, which are alternately laminated and fired at the same time , The application range is widening, and the demand for environment-friendly process is expanded. Therefore, studies for adding a new composition to existing piezoelectric ceramics are actively performed. For example, Korean Patent Publication No. KR 1994-0022936 discloses a piezoelectric ceramics composition having a high mechanical coupling coefficient.

An object of the present invention is to provide a piezoelectric ceramic composition, a piezoelectric device, and a method of manufacturing a piezoelectric ceramics using the piezoelectric ceramic composition, the piezoelectric device and the piezoelectric ceramic composition without deterioration in characteristics at the time of high-

According to the present invention (1-x) Pb (Mg 1/2 W 1/2) 0.03 (Ni 1/3 Nb 2/3) 0.09 (Zr y Ti 1 -y) 0.88 O 3 + a piezoelectric ceramic composition to which at least one sintering auxiliary of LiCO _{3 ,} CaCO _{3 ,} PbO, CuO and Fe ₂ O ₃ is added to the basic composition of xBiFeO ₃ (x = 0 or 0.015, y = 0.47 to 0.53) A piezoelectric element, and a method of manufacturing a piezoelectric ceramics.

The composition for piezoelectric ceramics according to the present invention is capable of low-temperature sintering, and the piezoelectric ceramics produced therefrom have improved structural characteristics, piezoelectric characteristics and dielectric properties.

FIG. 1 shows the X-ray diffraction pattern of the PMW-PNN-PZT ceramics composition according to the amount of Fe ₂ O ₃ added.
2 shows the density of a specimen according to changes in sintering temperature and addition of Fe ₂ O ₃ .
3a-e are SEM images showing the surface of each specimen to observe the microstructure of the PMW-PNN-PZT ceramics composition after calcination at 920 ° C with Fe ₂ O ₃ added.
Figs. 4 and 5 show changes in the electromechanical coupling coefficients k _P (FIG. 4) and k ₃₁ (FIG. 5) of the specimen with changes in the sintering temperature and the addition amount of Fe ₂ O ₃ .
6 and 7 is the piezoelectric constant of the specimen according to the change of the change in Fe ₂ O ₃ addition amount of the sintering temperature d ₃₃ (Fig. 6) and d ₃₁ (Fig. 7).
Figure 8 ₂ O ₃ changes in the sintering temperature and Fe (Ε _r ) at room temperature with changes in the addition amount.
FIG. 9 shows an X-ray diffraction pattern of a final PMW-PNN-PZT + BiFeO ₃ composition powder and a sintered pellet.
10 shows an SEM image of PMW-PNN-PZT + BiFeO ₃ ceramics.
11 shows the dielectric constant temperature dependence of PMW-PNN-PZT + BiFeO ₃ ceramics sintered at 920 ° C using a general oxide mixing method.
FIG. 12 shows X-ray diffraction patterns of PMW-PNN-PZT ceramics composition according to various sintering aid forms.
FIG. 13 shows X-ray diffraction patterns of PMW-PNN-PZT ceramics composition according to various sintering aid forms.
14 is a graph showing the relative dielectric constant according to the Zr / Ti ratio.
15 is a graph showing the electromechanical coupling coefficient according to the Zr / Ti ratio.
16 is a graph showing the piezoelectric constant according to the Zr / Ti ratio.
17 is a graph showing the coercive field according to the Zr / Ti ratio.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is capable of various modifications and various embodiments, and specific embodiments are illustrated in the drawings and described in detail in the detailed description. It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Hereinafter, the present invention will be described in more detail.

The present inventors selected PMW-PNN-PZT composition ceramics to develop low-temperature sintered piezoelectric ceramics. At least one of LiCO ₃ , CaCO ₃ , PbO, CuO and Fe ₂ O ₃ was used as a sintering aid. The sintering aids were investigated for their dielectric and piezoelectric properties at sintering temperatures of 900 ° C to 940 ° C by adding LiCO ₃ and CaCO _{3 ,} or by keeping PbO and CuO constant and varying the content of Fe ₂ O ₃ Respectively.

According to an aspect of the invention, (1-x) Pb ( Mg 1/2 W 1/2) 0.03 (Ni 1/3 Nb 2/3) 0.09 (Zr y Ti 1 -y) 0.88 O 3 + there is provided a piezoelectric ceramic composition to which at least one sintering auxiliary of LiCO _{3 ,} CaCO _{3 ,} PbO, CuO and Fe ₂ O ₃ is added to the basic composition of xBiFeO ₃ (x = 0 or 0.015, y = 0.47 to 0.53).

In one embodiment, a 0.2wt% LiCO ₃ and 0.25wt% CaCO ₃ may be added as the sintering aid.

In one embodiment, 0.3 wt% PbO, 0.3 wt% CuO, and 0.1 to 0.4 wt% Fe ₂ O ₃ may be added as the sintering aid.

According to another aspect of the invention, PbO, MgO, WO, NiO , Nb 2 O 5, of _{ZrO 2, TiO 2 (1-} x) Pb (Mg 1/2 W 1/2) 0.03 (Ni 1/3 Nb _2/3 ) _0.09 (Zr _y Ti _1-y ) _0.88 O ₃ + xBiFeO ₃ (x = 0 or 0.015, y = 0.47 to 0.53); The first calcination is performed by mixing MgO, WO, NiO, Nb ₂ O ₅ , ZrO ₂ , and TiO ₂ ; Mixing and crushing the first calcined sample and PbO so as to conform to the basic composition; Adding 0.3 wt% of PbO, 0.3 wt% of CuO, 0.1 to 0.4 wt% of Fe ₂ O ₃ , or 0.2 wt% of LiCO ₃ and 0.25 wt% of CaCO ₃ to the second calcined sample, mixing and crushing the same; And a step of sintering the mixture.

In one embodiment, the sintering can be performed at a temperature of 900 ° C to 940 ° C for 2 hours at a rate of 3 ° C / min.

According to another aspect of the present invention, there is provided a piezoelectric device including a piezoelectric ceramic composition according to an embodiment of the present invention. Examples of the piezoelectric element include, but are not limited to, a piezoelectric actuator, a piezoelectric resonator, a piezoelectric filter, a piezoelectric sensor, an ultrasonic transducer, and a high-efficiency capacitor.

A piezoelectric element according to an embodiment of the present invention includes a piezoelectric layer and an internal electrode layer. The piezoelectric layer includes a piezoelectric ceramic composition according to an embodiment of the present invention. When an electric charge is applied to at least one of the upper surface and the lower surface of the piezoelectric layer by the internal electrode layer, mechanical displacement occurs in the piezoelectric layer. The internal electrode layer is formed on at least one of the upper surface and the lower surface of the piezoelectric layer, and charges are applied to the piezoelectric layer. The internal electrode layer is connected to an external electrode layer to apply charge to the piezoelectric layer.

The internal electrode layer may include a silver (Ag) -palladium (Pd) alloy. In the case of simultaneously firing the piezoelectric layer and the internal electrode layer in the stacked piezoelectric element, since the internal electrode layer should not be oxidized at 1100 DEG C, which is the general firing temperature of the piezoelectric layer, the internal electrode layer contains a high content of palladium having a melting point of 1500 DEG C or higher.

According to an embodiment of the present invention, the content of palladium in the silver (Ag) -palladium (Pd) alloy constituting the internal electrode layer may be more than 0 wt% and less than 10 wt%. The piezoelectric ceramic composition according to an embodiment of the present invention can be sintered at a low temperature (950 DEG C or less), so that even when palladium of high price is limited to the above range, an internal electrode layer which is not deformed at the time of co- .

By doing so, since the piezoelectric element according to an embodiment of the present invention can be sintered at a low temperature, the content of palladium constituting the internal electrode layer can be reduced, and the manufacturing cost can be significantly reduced.

According to an embodiment of the present invention, the piezoelectric element may be a piezoelectric actuator. The actuator includes a piezoelectric layer including a piezoelectric ceramics composition capable of low temperature sintering according to an embodiment of the present invention and an internal electrode layer formed on at least one of an upper surface and a lower surface of the piezoelectric layer to apply charge to the piezoelectric layer, . The actuator causes piezoelectric deformation by the piezoelectric ceramic composition when a voltage is applied to the piezoelectric layer through the internal electrode layer. The configurations of the piezoelectric layer and the internal electrode layer have been described in detail in the description of the piezoelectric element, and detailed description thereof will be omitted.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Preparation method of specimen I

In order to develop low temperature sintered piezoelectric ceramics, PMW-PNN-PZT composition ceramics were selected, and to minimize heterogeneity due to the difference in reactivity between low-temperature sintering and B site components, PbO, CuO, Fe ₂ O ₃ was added. Here, PbO and CuO were kept constant and the content of Fe ₂ O ₃ was varied to investigate the dielectric and piezoelectric properties according to the sintering temperature from 900 º C to 940 º C.

The composition formula used in the experiment is shown in Equation 2 below.

(1-x) Pb (Mg 1/2 W 1/2) 0.03 (Ni 1/3 Nb 2/3) 0.09 (Zr y Ti 1 -y) 0.88 O 3 + xBiFeO ₃ (x = 0 or 0.015, y = 0.47 to 0.53) + 0.3 wt% PbO + 0.3 wt% CuO + zwt% Fe ₂ O ₃ (Z = 0 to 0.4 wt%) (Equation 2)

First, MgO, WO, NiO, Nb ₂ O ₅ , ZrO ₂ and TiO ₂ , which are B-site materials having a purity of 99% or more, were weighed to 10 ^-4 according to the composition and 3Φ zirconia balls And mixed and pulverized for 24 hours. The ball-milled sample was thoroughly dried for 12 hours or more in a constant-temperature drier and then calcined at 1100 ° C for 4 hours using an alumina crucible. To prepare the perovskite PMW-PNN-PZT specimen, the pre-calcined sample and the PbO weighed to the composition of the above formula 2 were mixed and pulverized for 24 hours. The mixed and pulverized samples were calcined at 750 ° C for 2 hours after drying. PbO, CuO, and Fe ₂ O ₃ were added to the second calcined sample as a sintering additive and mixed again and pulverized for 24 hours. PVA (5 wt% aqueous solution) was added to the dried sample and the molding pressure of 15 MPa And burned out at 600 ° C. for 3 hours. The specimens were sintered at a sintering temperature of 900 ℃ ~ 940 ℃ for 2 hours at 3 ℃ / min.

1) Measurement of Piezoelectric and Dielectric Properties of Specimen

The fired specimens were polished to 1 mm in order to measure the characteristics, and the Ag electrode was coated on both sides by screen printing method and then heat treated at 600 ° C. Thereafter, the specimen was subjected to polarization treatment by applying a DC electric field of 3 kV / mm for 30 minutes in silicone oil at 120 deg.

The dielectric constant of the sample was measured by measuring the capacitance at 1 kHz with an LCR meter (ANDO AG-4304). The microstructure and crystal structure of the specimen were measured by scanning electron microscope (SEM) and XRD -ray Diffraction). The particle size was calculated using the Linear Intercept Technical Method and measured with a charge tester (8000 piezo d ₃₃ tester) to investigate the piezoelectric constant (d ₃₃ ). The electromechanical coupling coefficient (k _P ) and the mechanical quality factor (Q _m ) were calculated by measuring resonance and antiresonance frequency and resonance resistance with an Impedance Analyzer (Agilent 4294A) according to IEEE regulations.

2) Sintering characteristics and structural characteristics of specimen

FIG. 1 shows the X-ray diffraction pattern of the PMW-PNN-PZT ceramics composition according to the amount of Fe ₂ O ₃ added. In the X-ray diffraction pattern shown in FIG. 1, all the specimens showed a typical pure perovskite structure, and the specimen without Fe ₂ O ₃ showed a slight secondary phase. On the other hand, as the amount of Fe ₂ O ₃ was increased, no secondary phase was found. These results suggest that complete solid phase reaction has been achieved.

As shown in FIG. 1, the (002) peak is increased with an increase in the amount of Fe ₂ O ₃ added, and the tetragonality is also increased.

2 shows the density of a specimen according to changes in sintering temperature and addition of Fe ₂ O ₃ . When the sintering temperature was 900 ° C, the density gradually decreased with increasing Fe ₂ O ₃ addition. It is considered that the density of the specimen is decreased because the sintering temperature of 900 º C is low for complete liquid sintering. When the sintering temperature was 920 ºC, the maximum density of the specimens with 0.3 wt% Fe ₂ O ₃ was found to be 7.94 g / ㎤. At 940 º C sintering temperature, it gradually increased as the addition of Fe ₂ O ₃ increased. However, when compared to the density at 920ºC, the overall density decreased. Therefore, it is considered that the sintering temperature of 920 ° C is the optimum sintering temperature, and that the density is lower than 920 ° C at 940 ° C.

3 (a) to 3 (e) are SEM images showing the surface of each specimen to observe the microstructure of the PMW-PNN-PZT ceramics prepared by firing Fe ₂ O ₃ at 920 ° C. When the addition amount of Fe ₂ O _{3 was} added at x = 0 (a), 0.1 (b), 0.2 (c), 0.3 (d), and 0.4 (e), the grain size of the specimen was 3.21 μm, 3.76 μm, 5.34 μm, μm and 4.55 μm, respectively, and the maximum value was 5.49 μm when the added amount was 0.3 wt%. These results indicate that Fe ₂ O ₃ and CuO added as sintering aids react with PbO to form eutectic points of PbO-Fe ₂ O ₃ (730 ° C) and PbO-CuO (680 ° C) phase, which leads to the liquid phase sintering, and it is believed that the grain growth is induced by densification due to the improvement of sinterability. The reason why the grain size decreased when Fe ₂ O ₃ was added in an amount more than 0.3 wt% was thought to be that Fe ₂ O ₃ was segregated at the grain boundary and suppressed grain growth.

3) Piezoelectric and dielectric properties of specimen

4 and 5 show changes in the electromechanical coupling coefficients k ₃₁ (FIG. 4) and k _P (FIG. 5) of the specimen with changes in the sintering temperature and the addition amount of Fe ₂ O ₃ . As the amount of Fe ₂ O ₃ added increases, the patterns of k _P and k ₃₁ changes tend to agree with each other. The electromechanical coefficient k and _P k is ₃₁ when the Fe ₂ O ₃ was added 0.2wt% at 900ºC sintering temperature, 0.39, to 0.68 exhibited a maximum value, respectively, k and _P k ₃₁ at 920ºC and 940ºC sintering temperature is Fe ₂ As the content of O ₃ increased, the content gradually increased, and the maximum value was 0.4, 0.69, 0.44 and 0.69, respectively, when 0.3 wt% was added. These results suggest that sintering aids with low melting point form liquid phase during sintering and sinterability is improved by liquid phase sintering, resulting in increased density and grain size. As shown in the SEM image of FIG. 3, it is believed that the electromechanical coupling coefficient is increased because the grain is grown and the domain switching and polarization efficiency becomes easier as the Fe ₂ O ₃ addition amount is increased. After that, it is considered that the decrease is due to a decrease in grain growth and a decrease in density.

6 and 7 is the piezoelectric constant of the specimen according to the change of the change in Fe ₂ O ₃ addition amount of the sintering temperature d ₃₃ (Fig. 6) and d ₃₁ (Fig. 7). The piezoelectric constants represent the magnitude of the displacement generated when an electric field is applied, and the piezoelectric constants d ₃₃ and d ₃₁ are similar to those of the electromechanical coupling coefficient (k _P ). The piezoelectric constants d ₃₃ and d ₃₁ were found to be 592 pC / N and 212 pC / N, respectively, when 0.2 wt% was added, when the firing temperature of the specimen was 900 ° C and the content of Fe ₂ O ₃ was increased. , And showed a tendency to decrease gradually when added more. And the piezoelectric constant d ₃₃ and d ₃₁ from 920ºC and 940ºC sintering temperature is Fe ₂ O showed the increment for as the addition amount of the increase is _3, the piezoelectric constant d ₃₃ and d ₃₁ was added at 0.3wt%, the sintering temperature of 920ºC The maximum value was found to be 662pC / N and 280pC / N at sintering temperatures of 632pC / N, 243pC / N and 940ºC, respectively. These results indicate that the piezoelectric constant is not high because the sintering is not performed sufficiently at 900 ° C due to the low temperature. On the other hand, high piezoelectric constant values at 920 ° C and 940 ° C are similar to those shown in FIG. 3, because the sintering property is improved by the liquid phase sintering, and the grain growth is increased. As a result, do. Also, it is suggested that the improvement of the piezoelectric properties is due to the increase of the value of the residual polarization and the dielectric constant according to reports that the values of the piezoelectric constant and the electromechanical coupling coefficient are proportional to the dielectric constant and the value of the remanent polarization.

Figure 8 ₂ O ₃ changes in the sintering temperature and Fe (Ε _r ) at room temperature with changes in the addition amount. The dielectric constant showed the same tendency as the results of electromechanical coupling coefficient (k _P ) and piezoelectric constant (d ₃₃ ). The more increase the amount of addition of Fe ₂ O ₃ was increased, the dielectric constant, Fe ₂ O ₃ is exhibited, 900ºC and 920ºC, 940ºC and respectively 2130, 2682, 2774 from the maximum value of the sintered specimen when added 0.3wt% . And when Fe ₂ O ₃ was added more than that, it was decreased. As can be seen from FIGS. 2 and 3, the dielectric constant was increased due to the increase in the density of Fe ₂ O ₃ , the decrease of the grain boundary of the low dielectric constant layer, and the decrease of the porosity due to the increase of the sintered density . The decrease in the dielectric constant seems to result from suppression of grain growth due to the presence of a liquid phase sintering additive which can not be solved at the grain boundary, which is a low permittivity layer at the grain boundary due to the solubility limit.

In the tables of the present invention, numerals for which units are not indicated represent ratios.

4) Fe ₂ O ₃  Low temperature sintering according to addition PMW - PNN - PZT  Characteristics of ceramics (sintering)

Results of XRD patterns All specimens exhibited a pure perovskite structure, in the microstructure of the Fe ₂ O ₃ additive amount of the sintered specimens at 920ºC, the average particle diameter size of the 0.3wt% of Fe ₂ O ₃ added to the specimen , The highest value of 5.49 μm was observed, and the tendency of decreasing tendency was shown.

The density of Fe ₂ O ₃ decreased with sintering at 900 ° C, but increased with sintering at 920 ° C and 940 ° C. In particular, when 0.3 wt% of Fe ₂ O ₃ was added at a sintering temperature of 920 ° C, a maximum value of 7.94 g / cm ³ was observed.

(K _P , k ₃₁ ), the mechanical quality factor Q _m , the piezoelectric constants (d ₃₃ , d ₃₁ ), the dielectric constant (∈ _r ) and the coercive field (E _c ) depend on the addition amount of Fe ₂ O ₃ could be obtained when it is in the sintered specimens from 940ºC, respectively 0.69, 0.44, 104.06, 662pC / N, 280pC / N, 2744, 0.3wt% to 10.42kV / cm is added, the Fe ₂ O ₃ was added 0.3wt% 920ºC 0.69, 0.40, 213.63, 632pC / N, 246pC / N, 2682 and 10.80kV / cm respectively for the sintered specimens.

5) Depending on the calcination temperature PMW - PNN - PZT  Changes in Ceramic Properties

The dielectric and piezoelectric properties of the PMW-PNN-PZT ceramics were investigated by varying the B-site calcination temperature and the second calcination temperature from 1070 ºC to 1100 ºC and 720 ºC to 780 º C, respectively, using the columbite precursor method. From the pattern, it can be seen that all the specimens exhibit a pure perovskite structure that is not on the pyrochlore phase. The average particle size of the specimens with the calcination temperature changes is 780 ° C at 2 ° C after B-site calcination at 1130 ° C It showed the tendency to increase with increasing the secondary calcination temperature. It showed the maximum value of 6.28μm in the specimen proceeding at 780ºC. This is a large increase compared to the standard size of the B-site calcination temperature of 1100 ° C and the average particle size of the second calcined 750 ° C sample of 4.88 μm.

The densities ρ, the electromechanical coupling factor k _p , the piezoelectric constant d ₃₃ and the dielectric constant ε _r of the specimens showed similar trends depending on the calcination temperature, while the k ₃₁ , d ₃₁ and S ₁₁ ^E showed a tendency to increase the B-site calcination temperature And then increased at the second calcination temperature of 780 ° C. For the optimum calcination temperature of B-site 1130 ºC, secondary calcination temperature 750 ºC and sintering temperature 720 ºC, the characteristic values were ρ = 7.78 g / cm ³ , k _p = 0.685, k ₃₁ = 0.41, d ₃₃ = 599 pC / d ₃₁ = 248 pC / N, 91.57 and E _C = 11.025 kV / cm.

The overall piezoelectric and dielectric properties of specimens sintered at 900 ºC and 920 º C with varying calcination temperature tended to decrease with increasing sintering temperature.

Method of preparing sample II

The basic composition formula of this experiment is as follows and specimens were prepared by general oxide mixing method.

_{0.985 [Pb (Mg 1/2} W 1/2) 0.03 (Ni 1/3 Nb 2/3) 0.09 (Zr 0 .5 Ti 0 .5) O 3 + 0.015BiFeO 3

+ 0.2 wt% Li ₂ CO ₃ + 0.25 wt% CaCO ₃ (Equation 3)

A sample having a purity of 99% or more such as PbO (99%), MgO (99%) and WO ₃ (99%) was weighed to 10 ^-4 g according to the composition formula, and acetone was dispersed as a dispersion medium using a 3 mm zirconia ball And then dried in a constant-temperature dryer at 80 ° C. The dried sample was calcined at a temperature of 850 ° C for 2 hours. The calcined sample was mixed with BiFeO ₃ And sintering additives such as Li ₂ CO ₃ and CaCO ₃ were weighed according to the composition formula and re-mixed and pulverized. The re-mixed and pulverized sample was dried, and 5 wt% aqueous solution of polyvinyl alcohol (PVA aqueous solution) was added to the sample, and molding pressure of 15 MPa was applied using a 17Φ molder. The molded specimens were burned out at 600 ° C for 3 hours to burn the PVA binder, and sintered at 920 ° C for 1 hour and 30 minutes at a rate of 3 ° C / mm. In order to measure the electrical characteristics of the specimen, the fired specimen was polished to a thickness of 1 mm, and then the Ag electrode was applied by screen printing. The specimen was heat treated at 600 ° C. for 10 minutes. And a direct current electric field of 3 kV / cm was applied for 30 minutes in the silicone oil at 120 캜 for polarization. After 24 hours of polarization, the resonance and antiresonance frequency and resonance resistance were measured using an impedance analyzer (Impedence analyzer, Agilent 4294) according to IEEE regulations, and the electromechanical coupling coefficient (k _P ) and the mechanical quality factor (Q _m ) was calculated. The microstructure and crystal structure of the specimens were observed by scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. The piezoelectric constant (d ₃₃ ) was measured using a Piezo-d ₃₃ meter (APC, YE 2730A). The dielectric constant was calculated by measuring the capacitance at a frequency of 1 kHz using an LCR meter (ANDO AG 4304) .

1) Dielectric and piezoelectric properties

FIG. 9 shows an X-ray diffraction pattern of the final PMW-PNN-PZT + BiFeO ₃ composition powder and a sintered pellet. All of the measured samples were sintered at 920ºC using general oxide mixing method. From the measured XRD pattern, it is assumed that the morphotrophic phase boundary (MPB) in which rhombohedral phase and tetragonal phase are coexisted. In the case of sintered pellet, the intensity of peak (200) Respectively. No pyrochlore was observed in both samples.

10 shows an SEM image of PMW-PNN-PZT + BiFeO ₃ ceramics. The measured specimens were fabricated at the sintering temperature of 920 ºC by the general oxide mixing method, and the average grain size of the specimens was 3.69 ㎛.

11 shows the dielectric constant temperature dependence of PMW-PNN-PZT + BiFeO ₃ ceramics sintered at 920 ° C using a general oxide mixing method. Temperature Curie was observed around 358ºC.

Table 2 shows the overall physical properties of PMW-PNN-PZT + BiFeO ₃ ceramics according to the manufacturing method. The piezoelectric and dielectric properties of the specimens sintered at 920 ºC were generally higher than those of the specimens prepared by the general sintering method, after calcining the B-site at 1100 ºC, (KP), dielectric constant (epsilon r), and piezoelectric constant (d ₃₃ ) of the B-site material tended to increase with calcination first. These results suggest that NiNb ₂ O ₆ produced by NiO and Nb ₂ O ₅ is more synthesized than B-site material first calcined by the general sintering method.

Method of preparing sample III

The basic composition formula of this experiment is as follows and specimens were prepared by general oxide mixing method. Except for the composition formula, the remaining method is the same as the above-mentioned " method of preparing specimen II ".

(1-x) Pb (Mg 1/2 W 1/2) 0.03 (Ni 1/3 Nb 2/3) 0.09 (Zr y Ti 1 -y) 0.88 O 3 + xBiFeO ₃ + 0.2wt% LiCO ₃ + 0.25 wt% CaCO ₃ (Equation 3)

1) Dielectric and piezoelectric properties

The composition for the piezoelectric actuator is normal d ₃₁ 190 or more, k ₃₁ 0.30 over, Ec 9.0㎸ / ㎝ enough for there to exhibit sufficient performance (1-x) Pb (Mg 1/2 W 1/2) 0.03 (Ni 1 / _{3 Nb 2/3) 0.09 (} Zr y Ti 1 -y) 0.88 O 3 + xBiFeO ₃ + 0.2wt% LiCO ₃ + The 0.25 wt% CaCO ₃ composition shows excellent properties over a wide range of x, y.

In the case of a haptic actuator requiring a small size and high vibration, a high dynamic range is required due to a high driving field, and a characteristic of d ₃₁ 220 or more, k ₃₁ 0.35 or more and Ec 11.0 kv / cm or more is required. , It is not possible to obtain a composition range satisfying all conditions in the case where BiFeO ₃ is not added. However, when Pb is substituted by 0.75 and 1.5 m / o BiFeO ₃ , Ec is increased in the total composition range as shown in FIG. 14 A composition region satisfying all conditions can be obtained. (Zr / Ti 49/51 to 50/50)

Fig. 14 shows the relative dielectric constant according to the Zr / Ti ratio, Fig. 15 shows the electromechanical coupling coefficient according to the Zr / Ti ratio, Fig. 16 shows the piezoelectric constant according to the Zr / Ti ratio, Which is a graph representing a coercive field, is supported by Table 3 above.

Table 3 shows that when x = 0, the section satisfying the characteristics of the general actuator is limited to y = 0.48 and 0.49, whereas when x = 0.0075 and x = 0.015, y = 0.48 to 0.51 , And satisfies the characteristic of the haptic actuator, which is a more demanding condition under the condition of y = 0.49 and 0.50.

ABO ₃ type perovskite when the bit structure is greater ²⁺ size in the A position ions, B location is the small 4 ⁺ ion sizes exist, and the, typically 4 ⁺ ions are present 3 ⁺ ions under the B site to Substituent acts as an acceptor and an oxygen vacancy is created to maintain the electrical neutrality of the entire crystal structure. Generally, there is a problem that an acceptor substitution increases the coercive field, decreases dielectric and piezoelectric characteristics, and lowers the reliability due to the movement of oxygen vacancies at high temperature and high electric field. On the other hand, when replacing the A site elements in 2 ⁺ a 3 ⁺ one element acting as a donor (donor), and the public Pb is generated to maintain the electrical neutrality of the entire crystal structure and increases the dielectric, piezoelectric properties. When such defects are present, the sinterability is improved because the material is generally moved well, and the piezoelectric properties are also improved. When Fe ₂ O ₃ , which is the acceptor, is added to PMW-PNN-PZT alone, the coercive field is improved, but the piezoelectric characteristics are sharply lowered due to the deformation of the crystal lattice. However, when Bi ₂ O ₃ is added at the same molar ratio It is considered that the deformation of the crystal lattice is minimized and the electromotive force is increased without deteriorating the piezoelectric characteristics as in the experimental results.

On the other hand, when Bi ₂ O ₃ and Fe ₂ O ₃ are added without being synthesized with BiFeO ₃ , there is a problem that the effect of improving Ec is low and a secondary phase is generated. It is difficult to control the number of defects of A site and B site equally. 12 and 13 show the results of X-ray diffraction patterns according to various sintering aids in PMW-PNN-PZT ceramics composition. As can be seen from the XRD patterns of Bi ₂ O ₃ and Fe ₂ O ₃ , -PNN-PZT, BiFeO ₃ has the same perovskite structure as that of the piezoelectric body. Thus, it is considered that there is no reduction in the piezoelectric characteristics due to minimization of the strain of the structure.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit of the invention as set forth in the appended claims. The present invention can be variously modified and changed by those skilled in the art, and it is also within the scope of the present invention.

Claims (10)

(1-x) Pb (Mg 1/2 W 1/2) 0.03 (Ni 1/3 Nb 2/3) 0.09 (Zr y Ti 1 -y) 0.88 O 3 + wherein at least one sintering auxiliary of LiCO _{3 ,} CaCO _{3 ,} PbO, CuO and Fe ₂ O ₃ is added to the basic composition of xBiFeO ₃ (x = 0 or 0.015, y = 0.47 to 0.53). The piezoelectric ceramic composition according to claim 1, wherein 0.2 wt% LiCO ₃ and 0.25 wt% CaCO ₃ are added as the sintering aid. The piezoelectric ceramic composition according to claim 1, wherein 0.3 wt% PbO, 0.25 wt% CuO, and 0.1 to 0.4 wt% Fe ₂ O ₃ are added as the sintering aid. A piezoelectric element comprising the piezoelectric ceramic composition according to any one of claims 1 to 3. 5. The method of claim 4,
The piezoelectric element includes:
A piezoelectric layer including the piezoelectric ceramic composition according to any one of claims 1 to 3; And
An internal electrode layer formed on at least one of an upper surface and a lower surface of the piezoelectric layer;
. 6. The method of claim 5,
Wherein the internal electrode layer comprises a (Ag) -palladium (Pd) alloy. The method according to claim 6,
Wherein the internal electrode layer has a content of palladium exceeding 0 wt% and equal to or less than 10 wt% in a silver (Ag) -palladium (Pd) alloy. 5. The method of claim 4,
Wherein the piezoelectric element is a piezoelectric actuator. PbO, MgO, WO, NiO, Nb 2 O 5, ZrO 2, the _{TiO 2 (1-x) Pb} (Mg 1/2 W 1/2) 0.03 (Ni 1/3 Nb 2/3) 0.09 (Zr y Ti _{1- y} ) _0.88 O ₃ + xBiFeO ₃ (x = 0 or 0.015, y = 0.47 to 0.53);
The first calcination is performed by mixing MgO, WO, NiO, Nb ₂ O ₅ , ZrO ₂ , and TiO ₂ ;
Mixing and crushing the first calcined sample and PbO so as to conform to the basic composition;
Adding 0.3 wt% PbO, 0.3 wt% CuO and 0.1 to 0.4 wt% Fe ₂ O _{3 ,} or 0.2 wt% LiCO ₃ and 0.25 wt% CaCO ₃ to the second calcined sample, mixing and grinding; And
Sintering the mixture
And a piezoelectric ceramic. 10. The method of manufacturing a piezoelectric ceramics according to claim 9, wherein the sintering is performed at a temperature of 900 deg. C to 940 deg. C for 2 hours at a rising / falling temperature gradient of 3 deg. C / min.

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